It is that simple. Pull the takedown pin and pivot pin, pull off your upper, and replace with a dedicated .22lr upper with its own bolt and magazine. There are a number of manufacturers out there who make dedicated uppers, and the .22lr ones might be easier to find right now in the panic buying.

There is also another option that uses your 5.56 or .223 upper. You replace your bolt carrier group with a unit, sometimes referred to as a Ceiner conversion, and utilize its magazine, and you are in business. To see what I mean, go out to CMMG's website and they offer some different models.http://www.cmmginc.com/category_s/1823.htm

I don't use either product, but I know some on here do and you will likely receive some recommendations shortly.